It is well known that the standard quantum field theory (QFT) is successful up to a certain energy scale \(\Lambda \ll M_{Pl}c^2\) , where \(M_{Pl}\)  is the Planck mass and \(M_{Pl}c^2 \sim 10^{19}~GeV\)  is the Planck energy.
As a result, QFT generally excludes the energy scale associated with quantum gravitational interactions.
A related issue is that in quantum gravity (QG), one expects quantum fluctuations of the background spacetime, whereas standard QFT assumes a fixed background spacetime on which quantum fluctuation of matter and gauge fields are studied.
As a result, a complete and consistent theory of QG is yet to be formulated, although there are promising candidate theories such as String Theory, Loop Quantum Gravity, Causal Dynamical Triangulations, Doubly Special Relativity (DSR) etc.
A consistent theory of QG may be a gateway to the unification of all fundamental forces of nature.
One shortcoming of all such theories is the complete absence of direct or
indirect experimental evidence in support of or contradicting them.
This being clearly undesirable, it is important to explore potential signatures of these theories in current or future experiments. This has been the subject of study of Quantum Gravity Phenomenology [1]}, [2]}.
